A thermal expansion valve is used to control the amount of refrigerant that flows to an evaporator in an HVAC system. Refrigerant flows through the thermal expansion valve before flowing into the evaporator. The thermal expansion valve reduces refrigerant pressure and thus reduces refrigerant saturation temperature. After the thermal expansion valve, the refrigerant enters into the evaporator and absorbs the heat from the air passing through the evaporator. Cooled air blows into the cabin, and superheated refrigerant exits the evaporator and enters into the compressor. Then the refrigerant changes to liquid after passing through the condenser and flows into the thermal expansion valve again. This is a repeating cycle.
When no air is passing through the evaporator, the thermal expansion valve still modulates the open and close positions, responding to ambient temperatures. This results in a cold thermal expansion valve dome. Afterwards, if there is air passing through the evaporator, it takes time for the cold thermal expansion valve dome to warm up in order to function properly. This delays supplying cool air to the cabin. The rear auxiliary thermal expansion valve tends to have this problem because of the rear auxiliary HVAC system's location. The slow response of the rear thermal expansion valve increases the time required to initiate cooling by the rear auxiliary HVAC system and affects the comfort of rear seat vehicle occupants.
Thermal expansion valves are normally provided within the HVAC housing and are exposed to flowing air in the housing that is blown by an air circulation fan. The air blown by the fan actuates the thermal expansion valve, allowing the thermal expansion valve to function more quickly when a request for cooling is sent to the auxiliary HVAC system. The thermal expansion valve may be located outside the casing of the rear auxiliary HVAC system due to accessibility and maintenance issues relating to auxiliary HVAC systems. The external thermal expansion valve is not exposed to air flowing through the HVAC housing when a request for air conditioning is received. The thermal expansion valve may be frozen by the refrigerant in the valve resulting in slow response by the auxiliary HVAC.
This disclosure is directed to the above problems and other problems as summarized below.